One Naval P-8 arrived in Argentina over the weekend, and another is arriving today. Additional rescue systems are now on their way, including a NATO submarine rescue system. Thus far, rough weather and high seas have been hindering the search, and hopes for the missing crew are fading.

The San Juan, a German-built sub, had a crew of 44—including Argentina's first woman submarine officer. The vessel went out of contact while en route from the islands of Argentina's Tierra del Fuego to the Armada Argentina's northern base at Mar del Plata. Previously, the modern diesel-electric sub, built in 1983 and put into service in 1985, went through a mid-life overhaul, completed in 2013. The sub's primary role has been intelligence collection, including surveillance of fishing grounds in Argentina's economic zone for illegal fishing operations.

The Navy's Poseidon patrol aircraft can deploy sonobuoys from the air to search for submerged submarines; these tube-launched buoys expand underwater into an array of sonar sensors that can get well below the surface layers of the ocean to either actively "ping" or quietly listen for sounds from a submarine. It also carries a powerful surface-scanning radar system, but the aircraft lacks the magnetic anomaly detection gear carried by its predecessor, the P-3 Orion.

The Navy patrol planes join the NASA P-3 Orion "flying lab" that had been in Argentina for Operation IceBridge. Other vehicles assisting the search include a Brazilian P-3 and EADS CASA C-295 multi-purpose aircraft, a Chilean CASA C-295, multiple Argentine naval and air force aircraft (including two Grumman S-2E Tracker submarine warfare aircraft and C-130s), and the British Navy's ice patrol ship HMS Protector.

In hopes of assisting if the submarine is located, a unit from the US Navy's Undersea Rescue Command (URC) deployed to Argentina on Saturday with a Submarine Rescue Chamber—a diving bell designed to dock with the escape hatch of a submarine in distress for crew rescues. The SRC, also known as a McCann Chamber, is essentially technology unchanged since World War II, and it's suited to shallow-water rescues. The Navy is also sending a Pressurized Rescue Module (PRM), a self-propelled rescue craft intended for deep-sea submarine rescues.

The US has additionally sent one torpedo-sized Bluefin 12D (Deep) UUV and three smaller OceanServer Iver3 580 UUVs from the Navy's Unmanned Undersea Vehicle Squadron 1, based in Pearl Harbor, Hawaii. These systems carry sonars that can be used to search for the sub on the bottom, helping to direct a rescue attempt. The Bluefin UUV, built by a unit at General Dynamics, was previously used as part of the search for Malaysia Airlines Flight 370 off the coast of Australia.

Regarding the weather issues, search efforts have been hampered by high waves and poor visibility in the Argentine Sea. A storm over the area is generating waves as high as 26 feet (8 meters) as shown in the video from the Argentine destroyer Sarandi posted by Armada Argentina today:

The high sea state may have contributed to the submarine's initial troubles. For the comfort of the crew and for the sake of speed, the San Juan would normally travel submerged at "snorkeling" depth, allowing the sub to run its diesel engines to power its electric drive and communicate through an antenna mast. The submarine also has an emergency position-indicating radio beacon (EPIRB) and a satellite communications buoy that can be deployed if the vessel is in distress.

Seven brief satellite calls over the past few days to Armada Argentina bases may have been made by the submarine's crew. But as of today, Argentine navy officials could not confirm if the calls were from the San Juan. "We are analyzing more closely to reliably determine that they weren't calls coming from the submarine," said Adm. Gabriel Gonzalez, chief of Mar del Plata Naval Base, in a statement to press this morning. Rain and high seas could interfere with satellite phone calls because of the relatively weak signal. The Argentine navy is seeking records from the satellite phone company to help locate where the calls were from.

Hope remains that the crew is alive and can be rescued. The sub would have oxygen for 10 days when submerged even without power. But the weather continues to pose significant challenges to a rescue attempt as well as the search, and it will be difficult to dock the Submarine Rescue Chamber to the San Juan's deck if the sub is on its side or at an angle on the bottom.

Update, 2:55 PM EST: Argentine navy officials have reported that sounds have been detected that may be the crew of the San Juan signaling underwater for help. The search area has been reduced to a 35-square-mile area about 330 miles off the southern Argentine coast.